Copyright law varies by country (e.g., fair use in the US for archival purposes vs. strict laws in Germany/Japan). The emulation community generally supports preservation. If you own the original disc, sourcing a GDI of that disc is legally arguable as a backup. Downloading GDI files for games you do not own is copyright infringement.
GDI File Extension: What Is It & How To Open It? - Solvusoft dreamcast roms gdi
When you download or dump a game in GDI format, you will typically receive a folder containing: Copyright law varies by country (e
5+ Comprehensive Guides to Burning Dreamcast ROMs onto CD-Rs Copyright law varies by country (e.g.